The present disclosure relates to a method of manufacturing an abrasive particle, and more particularly, to methods of manufacturing an abrasive particle and a polishing slurry capable of enhancing the polishing rate of a target layer to be polished and decreasing micro scratches.
A chemical mechanical polishing (CMP) process is conducted by a polishing pad equipped in a polishing apparatus after a slurry containing abrasive particles is put on a substrate. In this regard, the abrasive particles mechanically polish a surface of the substrate with a pressure applied from the polishing apparatus, and chemical components contained in the slurry chemically react with the surface of the substrate to chemically remove a portion of the surface of the substrate. The abrasive particles may include, for example, ceria (CeO2), and the like, and may be selectively used according to target layers to be polished.
Meanwhile, in existing methods of manufacturing a NAND flash memory, the shallow trench isolation (STI) process in which a nitride layer is used as a hard mask in order to form a device isolation layer is conducted. That is, a nitride layer is first formed on a substrate, a trench is formed on a predetermined region of the substrate, an oxide layer is formed to fill the trench, and the oxide layer is polished to form a device isolation layer. In this regard, the oxide is polished using a dry ceria slurry capable of securing a high polishing selection ratio of the oxide layer and the nitride layer until the nitride layer is exposed, and then the remaining nitride layer is removed by a wet etching. However, when the device scale is reduced to 20 nm or less, loss of the oxide layer occurs during the wet etching of the nitride layer and leakage current sharply increases between devices due to the loss of the oxide layer, so that the devices may be erroneously operated.
To solve the above-described problems, a new CMP process has been developed, which uses a polysilicon layer used as a floating gate as a polishing stop layer instead of using the nitride layer as a hard mask. That is, a tunnel insulating layer and a polysilicon layer are formed on a substrate, the polysilicon layer, the tunnel insulating layer and the substrate are sequentially etched to form a trench, an insulating layer is formed to fill the trench, and then the insulating layer is polished until the polysilicon layer is exposed, thereby forming a device isolation layer. Herein, when surface defects, particularly, micro scratches are generated in the polysilicon layer used as a floating gate after the CMP process, the generated micro scratches have an influence on the threshold voltage of devices. Then, since the dry ceria particles have an angular grain shape and a wide grain size distribution as shown in FIG. 1 due to limitations of the manufacturing method, the application of such dry ceria particles to the CMP process for forming NAND flash memory devices inevitably creates micro scratches. Compared with the dry ceria particles, since wet ceria particles have a relatively narrow grain size distribution, do not create particles having a large secondary particle diameter, and have a polyhedral structure as shown in FIG. 2, the wet ceria particles may greatly improve micro scratches compared with the dry ceria particles. However, when the size of the wet ceria particles is not larger than 40 nm, the polishing rate of the insulating layer is very low, and the size of the wet ceria particles is 100 nm or larger, the number of micro scratches is sharply increased due to sharp crystal faces of the polyhedral structure.
Meanwhile, U.S. Pat. Nos. 6,221,118 and 6,343,976 disclose a method of synthesizing a ceria particle used for polishing an insulating layer in a shallow trench isolation (STI) process, and a substrate polishing method using the same. The related arts also disclose an average particle diameter and a particle diameter distribution range of abrasive particles required for the characteristics of a slurry for polishing an insulating layer. However, since the ceria particles disclosed in the above-described related arts substantially include macro abrasive particles causing micro scratches, the ceria particles fail to suppress creation of micro scratches.